The present invention relates to improvements in locks, and more particularly to an improved lock mechanism for safely locking doors such as trailer-tractor vehicle doors in a secure manner so that primarily they can be opened only by connection with the air system of the vehicle.
Trailer-tractor doors are commonly latched in a closed position by manually operated latches accessible from the rear of the trailer-tractor where the doors are either swung open or raised. For security to prevent unauthorized opening, the release handles are padlocked or locked in a manner to require opening with a key or combination. However, in the absence of the driver, the padlock or other locking device can be broken, the doors opened and the contents tampered with or stolen. Security of the doors is very important inasmuch as the contents can frequently be valuable or can be of a nature such that positive prohibition from stealing is of the essence, such as when the trailer-tractor may contain equipment which must have commercial or military security or secrecy.
As an example of the lack of security provided by conventional padlocking, insurance companies and trucking companies have found that a padlocked trailer-tractor door lock can be broken and the contents of a trailer-tractor or truck stolen or partly stolen within the very short time when the truck stops at a traffic light. While the features of the invention as will be described herein are particularly well suited for use with trucks or trailer-tractor type vehicles, it will be appreciated by those versed in the art that the features may be employed for securely locking other vehicle doors such as doors on railroad cars.
In addition to externally padlocked door latches, attempts have been made to provide for internal door locks, but the operator for such locks must still be provided with a locking means such as a padlock. A feature of the present invention is the provision of a lock which is air operated so that it can be used by vehicles with an air braking system and principally operated only with high pressure air.
An object of the present invention is to provide a security locking device designed primarily to be utilized in locking trailer doors on tractor-trailer vehicles which can be used by vehicles with an air braking system.
A further object of the invention is to provide a particularly safe and secure lock mechanism for doors wherein the locking mechanism is housed in a tamper-proof box wherein access to the locking system and to the box is afforded by the application of air pressure. A further object of the invention is to provide a locking system which cannot be tampered with and which is particularly useful in a truck or tractor-trailer system inasmuch as access is under positive control of the driver.
Other objects, advantages and features will become more apparent with the teaching of the principles of the invention in connection with the disclosure of the preferred embodiments in which: